VIII. DIEN THE KICH THICH CAM GlAC THAN THE 1 Dai cifdng
3. Sinh ly difcfng dan truyen cam giac
a. Dieting dan truyen
- Dtfdng dan truyen cam giac sau co y thtic: cac sdi true (axon) cua neuron cam giac thti nhat la nhting sdi th&n kinh nhom Ia va II, chting co dtfdng kmh 4 - 2 0 |im, co bao myelin, toe do dan truyen nhanh (30 - 110 m/s). Dtfdng dan truyen cam giac sau nay co y nghla rat ldn trong stf hinh thanh cac dien the kich thich cam giac than the.
- Dtfdng dan truyen cam giac sau khong y thtic: di qua re sau vao sting sau tuy song noi tiep vdi neuron 2. Sdi true cua neuron 2 di ra cot ben cung ben tao thanh bo Flechsig (bo tieu nao thang) hoac bat cheo qua dtfdng gitia sang ria cot trang ben doi dien tao thanh bo Gowers (bo tieu nao bat cheo), hai bo nay di len tren va tan cung d thuy giun tieu nao.
- Dtfdng dan truyen cam giac dau va nhiet do: cac sdi true cua neuron 1 cung di qua re sau vao sting sau tuy song, tti day neuron 2 bat dau va di cheo qua mep xam trtfdc sang cot ben doi dien tao thanh bo gai - thi, bo nay di tiep len doi thi, tti doi thi neuron 3 bat dau va di tiep len trung khu vo nao cam giac.
Cac sdi true cua diidng dan truyen nay thuoc cac sdi nhom III va IV co diidng kinh nho hdn 4|am, khong co bao myelin.
b. Sinh ly dan truyen xung dong than kinh.
Sii d in truyen cam giac tii thu the len trung khu phan ti'ch cam giac d vo nao thiic chat la sii dan truyen cac xung dong than kinh. Cd che cua sii dan truyen nay la mot qua trinh lan truyen hoat dong khu ciic cua sdi te bao than kinh. Khi tai mot diem cua te bao hoac cua sdi than kinh bi ki'ch thi'ch se xay ra sii khii ciic mang te bao. Sii khii ciic nay dUdc tap cong theo ca thdi gian va khong gian den khi tao ra dU dc mot dien the khu ciic du ldn (tiic la tao ra mot dien the hoat dong) tai diem do thi no se dU dc truyen di doc te bao hoac sdi day than kinh tao nen mot xung dong than kinh (doi vdi te bao va sdi than kinh thi sii chenh lech giiia dien the trong va ngoai te bao dat khoang - 20pV (binh thiidng la -70 den -90 |iV) se gay khu ciic te bao (dien the ngiidng) va tao nen mot dien the hoat dong). Sii dan truyen xung dong than kinh tuan theo quy luat "tat ca hoac khong". Cac xung dong th&n kinh dU dc tao ra se lan ra cac vung xung quanh mang te bao hay doc sdi true tao ra dien the hoat dong d vung ke can, sii lan truyen nay cif tiep tuc nhu vay. Doi vdi sdi than kinh cd bao myelin cac xung dong dan truyen theo kieu "nhay coc" qua cac eo Ranivier nen toe do dan truyen ldn hdn rat nhieu so vdi c a c sdi khong co bao myelin.
4. Cd sd ly thuyet cua phiidng phap ghi dien the
kich thich cam giac than the.
De tao diidc song SEP, ta kich thich cac sdi hiidng tam cua cd va da hoac triic tiep len day than kinh. Khi kich thich mot day than kinh hon hdp thi xung dong dan truyen
theo cac sdi khac nhau deu dupe phong chieu len vo nao. Tren dUdng dan truyen do ta dat cac dien cUc tai cac vi tri khac nhau va se ghi diidc cac dien the khac nhau.
Theo phan loai cua Lloyd, cac sdi hudng tam loai la va II co dUdng ki'nh tii 4 - 20|iV gom cac sdi cam giac rung, de ep, cam giac cua sdi thoi cd (sd cap va thti cap), sdi cua thu the Golgi. Cac spi nhom III va IV co dUdng ki'nh nho (gom cac sdi dan truyen cam giac dau va nhiet do) co ngUdng ki'ch thi'ch cao hdn.
Khi ki'ch thi'ch day than kinh gitia hoac day than kinh chay sau, ngUdi ta co the ghi dupe rat nhieu song dap Ung cua dien the ki'ch thi'ch tren cac chang dan truyen qua re than kinh (dien the cua re than kinh), qua tuy song (dien the cua tuy song), len cac cau true dUcfi vo (dien the cua cac cau true dudi vo), roi len vo nao (dien the cua vo nao cam giac dac hieu).
Cac thanh phan dien the du6i vo co bien do nho nhat (<l|aV) co dac ti'nh ben vting, khong phu thuoc vao y thUc cua benh nhan. Nhung cac thanh phan muon cua dien the thi co bien do ldn hdn va phu thuoc vao y thUc cua benh nhan (chi can thieu tap trung tU tudng la dan den sU thay doi dien the).